The effect of uniaxial pressure on the ferroelectric phase transition of TGSe crystals

Abstract

Isobaric studies of the influence of uniaxial pressure on the transitions of pure TGSe crystals for the three directions x, y, z (a * , b, c) are reported. The critical exponents, β, δ and γ , from dielectric constant and hysteresis loop measurements, as well as the coefficients ξ and ζ of the fourth and sixth powers of P in the free-energy expansion under uniaxial pressure were determined. It has been found that uniaxial pressure applied along the a * -axis keeps the transition near a tricritical point for 0 < X < 200 bar, but that when it is applied along the band c-axes it strengthens the second-order phase transition behaviour. The tricritical behaviour of TGSe crystals is discussed and a possible driving mechanism for the change in order of the phase transition is proposed. † We are not concerned here with ferroelastic crystals, for which several examples of a TCP or Lifshitz TCP (LTCP) are known and have been studied both experimentally and theoretically.

Dielectric properties of fine-grained triglycine sulphate (TGS)

“…Thus, under hydrostatic pressure of 1.5 GPa, ΔT c should amount to 30 K. Following other authors [21], it can be speculated that the effect of uniaxial pressure is equivalent approximately to that of a tenth of the hydrostatic pressure and ΔT c~+ 3 K can be expected due to the powder pressing, which is of the order of magnitude of the value found experimentally (Fig. 4).…”

Influence of Uniaxial Pressure on the Phase Transition of Partially Deuterated Glycinium Phosphite

“…Effect of uniaxial pressure on the phase transition temperature of TGS was reported by Imai [13] with a rate of -6.7 K/kbar, -9.1 K/kbar and 19.0 K/kbar for a * -, b-and c-axis, respectively. Koralewski et al [14] was reported in the case of TGSe with a rate of -15.9 K/kbar, -8.7 K/kbar and 28.3 K/kbar for a * -, b-and c-axis, respectively.…”

Lattice mediated interactions and ferroelectric anomalies in the crystal (CH3NH3)5Bi2Cl11(PMACB)

“…A hydrostatic pressure applied to the crystal does not change this ratio (Gesi et ul., 1995), which could speak against the tricritical point behaviour. It is nevertheless possible that an uniaxial stress along the crystallographic direction [OOl] would be more efficient Downloaded by [University of Western Ontario] at 20:17 17 November 2014 in displacing the system from the tricritical point in analogy with TGSe crystal (Koralewski et al, 1997). It is worth noting that so-called "logarithmic corrections" to the critical behaviour also predict the ratio -4 for the inverse susceptibilities even in the case of an usual critical point (see for example Binder et al, 1976).…”